Conventionally, adhesive tapes comprising a tape substrate (hereinafter to be also simply referred to as a substrate) composed of polyvinyl chloride (hereinafter to be referred to as PVC) have been widely used as insulating tapes for electric equipment used in the fields of vehicles (e.g., automobile, train, bus and the like), aircraft, ship, house, plant and the like because they are superior in mechanical properties (particularly flexibility and stretchability), flame resistance, resistance to thermal deformation, electrical insulation and the like, and relatively economical. Particularly, adhesive tapes to be wound around wire harness used for electric wires in automobile and the like, coils for household electric appliances, and electric wires and the like are required to show high flame resistance (oxygen index of not less than 25%) and high resistance to thermal deformation. To meet such requirements, adhesive tapes using PVC as a substrate have been widely used.
Under the circumstances, a number of substrates for adhesive tape (alternative technique), which use a relatively flexible olefin resin, have been considered instead of flexible PVC suspected of generating a harmful gas. To confer flame resistance, however, addition of a large amount of a flame retardant is necessary since polyolefin resins are flammable by nature. Considering the environmental aspects, in particular, inorganic metal compounds such as metal hydrate and the like are often added, since they produce highly safe combustion gas. To achieve high flame retardancy, however, a large amount of an inorganic metal compound needs to be added, which in turn produced problems such as lower mechanical properties, impaired appearance, degraded processability and like.
As to the lower mechanical properties, the Applicant of the present application proposed a method of suppressing the degradation of mechanical properties, which includes treating the surface of an inorganic metal compound with a silane coupling agent and adding a thermoplastic resin containing a carbonylic oxygen atom in the molecular skeleton of EVA and the like (JP-A-2001-311061). Moreover, the Applicant proposed a method of further enhancing the mechanical properties by adding a salicylic acid compound. In this method, an aminosilane treatment was most effective among silane coupling treatments (JP-A-2006-193565).
However, since these methods require a silane coupling treatment, compositions problematically show poor metal release property (i.e., releasability from metal) and significantly impair the processability. Moreover, since the silane coupling treatment reduces the flowability of resin compositions, it problematically degrades the appearance of molded products. In particular, an aminosilane treatment significantly degrades the processability.
Examples of the method for enhancing the resistance to thermal deformation of this kind of resin composition include a method comprising irradiation of ionization radiation, a method comprising forming a crosslinking structure by adding a crosslinking agent such as an organic peroxide and the like (e.g., di-cumyl peroxide and the like) in advance to a resin composition and applying vapor heating and the like after molding, and the like. These methods problematically increase the number of production steps and production costs, and therefore, are difficult for practical application.